provider/aws: Allow Instance to be computed in EIPs

[catsby]

If you have an EIP attached to a network interface, which then has an Instance attached to it, Terraform plans will want to remove the instance attachment of the EIP, even though there is no explicit connection made by the user:

resource "aws_eip" "nat_ip" {
  network_interface = "${aws_network_interface.nat_eni.id}"
}

resource "aws_network_interface" "nat_eni" {
    # other attributes
  attachment {
    instance = "${aws_instance.nat.id}"
    device_index = 1
  }
}

resource "aws_instance" "nat" {
  ami = "ami-21f78e11"
    # other attributes
}

After applying, future plans will show this:

~ aws_eip.nat_ip
    instance: "i-<instance_id>" => ""

This PR make instance a computed attribute, and also removes the ConflictsWith restraint from network_interface. Oddly enough, the AssociateAddress API docs say you can't have both of these specified, but we do here and get no error.

Fixes #2952

[stack72]

yay! This looks such a simple change :) Thanks @catsby

[phinze]

will want to destroy the instance associated with the EIP

This just means "remove the instance attachment of the EIP" not "destroy the instance" right?

Oddly enough, the AssociateAddress API docs say you can't have both of these specified, but we do here and get no error.

I think they're both populated in the Describe API call but you can't send both of them when you Associate - so I think ConflictsWith still makes sense for a config perspective?

Or maybe I'm misunderstanding how we have both of them specified here. Maybe you can 'splain me more?

[stack72]

@phinze yes, it will remove the attachment

[phinze]

@stack72 cool - for a second i was like "what are you doing, Terraform?!" 😅

[catsby]

This just means "remove the instance attachment of the EIP" not "destroy the instance" right?

haha, yeah that's my bad. It will not destroy the instance. I updated to match your wording 😄

but you can't send both of them when you Associate - so I think ConflictsWith still makes sense for a config perspective?

well, you can send them both..

2015/08/20 11:34:32 terraform-provider-aws: 2015/08/20 11:34:32 [DEBUG] EIP Allocate: {
2015/08/20 11:34:32 terraform-provider-aws:   AllocationId: "eipalloc-7cb33619",
2015/08/20 11:34:32 terraform-provider-aws:   Domain: "vpc",
2015/08/20 11:34:32 terraform-provider-aws:   PublicIp: "54.191.221.60"
2015/08/20 11:34:32 terraform-provider-aws: }
2015/08/20 11:34:32 terraform-provider-aws: 2015/08/20 11:34:32 [INFO] EIP ID: eipalloc-7cb33619 (domain: vpc)
2015/08/20 11:34:32 terraform-provider-aws: 2015/08/20 11:34:32 [DEBUG] EIP associate configuration: {
2015/08/20 11:34:32 terraform-provider-aws:   AllocationId: "eipalloc-7cb33619",
2015/08/20 11:34:32 terraform-provider-aws:   InstanceId: "i-f14bfa37",
2015/08/20 11:34:32 terraform-provider-aws:   NetworkInterfaceId: "eni-30cf9979"
2015/08/20 11:34:32 terraform-provider-aws: } (domain: vpc)
2015/08/20 11:34:33 [DEBUG] EIP describe configuration: {
  AllocationIds: ["eipalloc-7cb33619"]
} (domain: vpc)
...
[root debug stuff]
...
2015/08/20 11:34:33 waiting for all plugin processes to complete...
Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

but it seems to favor the InstanceId and attach the EIP to that, and uses the default ENI .. basically ignoring the NetworkInterfaceId you sent...

Unfortunately, I can't have both the ConflictsWith on network_interface and Computed on instance, Terraform won't let me. Thoughts, @phinze ?

[jszwedko]

Would documentation be sufficient for discouraging the user from setting both @phinze @catsby ? Or maybe a warning?

I guess it might be nicer to have ConflictsWith ignore computed attributes.

[phinze]

Yeah I think for now we just document the limitation and then ship it. 👍 🚢

[catsby]

Documented the limitation/behavior in 9d973f1, pull this in now

[ghost]

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